Index pattern: "_id" field marked as aggregatable

[flash1293]

Kibana version: master

Describe the bug:

When creating an index pattern, _id is mapped as an aggregatable string field. However it's not actually aggregatable and using it e.g. in a terms operation will result in an Elasticsearch error

Steps to reproduce:

1. Go to Visualize
2. Configure bar chart based on logs sample data
3. Add x axis terms aggregation based on _id field
4. Apply
5. Error toast is shown

Expected behavior:
_id should not be shown in the dropdown at all

Screenshots (if relevant):

Errors in browser console (if relevant):

{
   "statusCode":400,
   "error":"Bad Request",
   "message":"status_exception",
   "attributes":{
      "error":{
         "type":"status_exception",
         "reason":"error while executing search",
         "caused_by":{
            "type":"search_phase_execution_exception",
            "reason":"all shards failed",
            "phase":"query",
            "grouped":true,
            "failed_shards":[
               {
                  "shard":0,
                  "index":"kibana_sample_data_logs",
                  "node":"6l5pPGD_TPiXOil7W2YxsA",
                  "reason":{
                     "type":"illegal_argument_exception",
                     "reason":"Fielddata access on the _id field is disallowed, you can re-enable it by updating the dynamic cluster setting: indices.id_field_data.enabled"
                  }
               }
            ],
            "caused_by":{
               "type":"illegal_argument_exception",
               "reason":"Fielddata access on the _id field is disallowed, you can re-enable it by updating the dynamic cluster setting: indices.id_field_data.enabled",
               "caused_by":{
                  "type":"illegal_argument_exception",
                  "reason":"Fielddata access on the _id field is disallowed, you can re-enable it by updating the dynamic cluster setting: indices.id_field_data.enabled"
               }
            }
         }
      }
   }
}

Provide logs and/or server output (if relevant):

Any additional context:

The code deriving the index pattern fields should probably be adjusted to not mark _id as aggregatable.

[elasticmachine]

Pinging @elastic/kibana-app-arch (Team:AppArch)

[mattkime]

this is an ES bug - elastic/elasticsearch#62897